1. Field of the Invention
This invention relates to a flexible bag type filter for cleaning gaseous streams containing suspended solid particulates.
2. Description of the Prior Art
In the carbon black industry, as well as numerous others, there is a need for removing entrained solid particulates from gaseous streams. Carbon black products, for example, are essentially recovered from the aerosol effluent of the furnace by means of bag filters. In this type of filtering operation, the furnace effluent is passed into a battery of suspended bags wherein the carbon black collects upon the interior surface thereof and is periodically removed during the cleaning cycle by contacting the exterior of the bag with a moderately pulsating repressuring gas. Because of the corrosive nature of the carbon black aerosols and the elevated temperature at which they must be filtered, necessitates the use of fiberglass cloth for fabricating the bags. While fiberglass cloth exhibits very low impact strength and abrasion resistance, it nonetheless can be satisfactorily used in the aforesaid primary recovery system since the cloth can cope with the relatively gentle flexing action to which it is subjected in the aforementioned cleaning cycle.
Besides the primary recovery system, filter bags are likewise used in secondary recovery systems in the carbon black industry, that is, in the processing of nuisance streams. Nuisance streams are those arising in the packing of the carbon black and like operations as well as in various drying operations such as encountered in drying pelleted carbon black. Heretofore, synthetic fiber cloth and felt have been almost exclusively used to fabricate bags for secondary filtering operations because of the demands upon the filter medium posed by this type of a system. Such a system differs from a primary recovery one in several important aspects. Firstly, the filter bag is supported by a wire mesh frame and the stream to be cleansed is passed through the bag from the exterior thereof. Secondly, a different method is employed for removing accumulated layers of carbon black during the cleaning cycle. This is achieved in the off-filtering or cleaning cycle by directing blasts of compressed air into the interior of the individual bags.
For reasons which need not be gone into here, the ambient temperature of the aforementioned carbon black nuisance streams has already reached a point where now such streams are having a noticeably deleterious effect on synthetic fiber type of filtering media. This, of course, suggests the use of fiberglass cloth filter bags for ameliorating the situation. But the problem with this approach is premature bag failure insofar as bag life is often measured in hours in the type of filtering operation concerned. It is, accordingly, the object of this invention to provide a fiberglass bag filter construction which can be used in the pulse-jet type of filtering operation whereby the bag life expectancy will exceed that of the synthetic fiber bags employed under the same demanding temperature and corrosive environment.